XIO2001IPNP datasheet(57/145 Pages) TI2

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Table 8-27. Bridge Control Register Description (continued)

BIT

FIELD NAME

ACCESS

DESCRIPTION

MAM

Master abort mode. This bit controls the behavior of the bridge when it receives a master

abort or an unsupported request.

0 = Do not report master aborts. Returns FFFF FFFFh on reads and discard data on

writes (default)

1 = Respond with an unsupported request on PCI Express when a master abort is

received on PCI. Respond with target abort on PCI when an unsupported request

completion on PCI Express is received. This bit also enables error signaling on

master abort conditions on posted writes.

VGA16

VGA 16-bit decode. This bit enables the bridge to provide full 16-bit decoding for VGA I/O

addresses. This bit only has meaning if the VGA enable bit is set.

0 = Ignore address bits [15:10] when decoding VGA I/O addresses (default)

1 = Decode address bits [15:10] when decoding VGA I/O addresses

VGA

VGA enable. This bit modifies the response by the bridge to VGA compatible addresses. If

this bit is set, then the bridge decodes and forwards the following accesses on the primary

interface to the secondary interface (and, conversely, block the forwarding of these

addresses from the secondary to primary interface):

• Memory accesses in the range 000A 0000h to 000B FFFFh

• I/O addresses in the first 64 KB of the I/O address space (address bits [31:16] are

0000h) and where address bits [9:0] are in the range of 3B0h to 3BBh or 3C0h to

3DFh (inclusive of ISA address aliases – address bits [15:10] may possess any

value and are not used in the decoding)

If this bit is set, then forwarding of VGA addresses is independent of the value of bit 2

(ISA), the I/O address and memory address ranges defined by the I/O base and limit

registers, the memory base and limit registers, and the prefetchable memory base and limit

registers of the bridge. The forwarding of VGA addresses is qualified by bits 0 (IO_ENB)

and 1 (MEMORY_ENB) in the command register (offset 04h, see Section 8.4.4).

0 = Do not forward VGA compatible memory and I/O addresses from the primary to

secondary interface (addresses defined above) unless they are enabled for

forwarding by the defined I/O and memory address ranges (default).

1 = Forward VGA compatible memory and I/O addresses (addresses defined above)

from the primary interface to the secondary interface (if the I/O enable and memory

enable bits are set) independent of the I/O and memory address ranges and

independent of the ISA enable bit.

ISA

ISA enable. This bit modifies the response by the bridge to ISA I/O addresses. This applies

only to I/O addresses that are enabled by the I/O base and I/O limit registers and are in the

first 64 KB of PCI I/O address space (0000 0000h to 0000 FFFFh). If this bit is set, then the

bridge blocks any forwarding from primary to secondary of I/O transactions addressing the

last 768 bytes in each 1-KB block. In the opposite direction (secondary to primary), I/O

transactions are forwarded if they address the last 768 bytes in each 1K block.

0 = Forward downstream all I/O addresses in the address range defined by the I/O

base and I/O limit registers (default)

1 = Forward upstream ISA I/O addresses in the address range defined by the I/O base

and I/O limit registers that are in the first 64 KB of PCI I/O address space (top 768

bytes of each 1-KB block)

SERR_EN

SERR enable. This bit controls forwarding of system error events from the secondary

interface to the primary interface. The bridge forwards system error events when:

• This bit is set

• Bit 8 (SERR_ENB) in the command register (offset 04h, see Section 8.4.4) is set

• SERR is asserted on the secondary interface

0 = Disable the forwarding of system error events (default)

1 = Enable the forwarding of system error events

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XIO2001

SCPS212J – MAY 2009 – REVISED JANUARY 2021

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